(1) Field of the Invention
The invention pertains to a device for sharpening knives. More particularly the invention provides a sensor for measuring contact between the knife requiring sharpening and the sharpening tool such as a grinding belt, grinding wheel or the like along with the relative movement between the sharpening tool and the knife disposed in a knife mount for positioning the knife.
(2) Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Sharpening machines are available on the market for sharpening knives in meat processing machines, such as meat grinders, cutters or the like, in which a knife can be sharpened by hand with a respective sharpening tool, e.g., a belt grinder or grinding wheel. Guiding aids for manual sharpening have been disclosed in publication DE 198 36 804, for example, and are used to facilitate manual sharpening while reducing the danger of accidents.
In addition, semiautomatic machines are available on the market for sharpening knives in meat processing machines, in which the contour of the knife, e.g., a cutter knife, is automatically traversed. Since the first so-called advance, i.e., the path traversed until the sharpening tool contacts the knife, varies depending on how worn the cutter knife is, the first advance is initiated manually as before, and the operator determines when to stop the movement of the knife against the cutting tool by his or her sense of hearing.
Since the knives are routinely sharpened after reaching a respective level of wear, and the outer contour of the knives changes dimensions as they experience wear and must therefore be resharpened, there is no fixed reference point for moving the knife against a cutting tool, which is why knives for meat processing machines have heretofore not been automatically resharpened.
Apart from the personnel input, manual or semiautomatic processing is also disadvantageous because movement toward the cutting tool is imprecise. The incidental noises usually prevalent at such processing facilities are highly disruptive to operators relying on their sense of hearing, so that the actual point where contact is made between the sharpening tool and cutting tool is often exceeded. On the one hand, this results in an excessive abrading of the knife, thereby respectively diminishing the service life of both the knife and sharpening tool. In addition, the sharpening tools for sharpening cutter knives are designed precisely in such a way as to move evasively when a certain sharpening pressure is exceeded, i.e., the application force of the knife against the sharpening tool. As a result, when the knife is pressed too strongly against the sharpening tool, the sharpening procedure no longer centers on the cutting edge of the knife, and hence no longer sharpens it.
Therefore, the object of the invention is to propose a device that enables the reliable movement of the sharpening tool against knives of meat processing machines to be resharpened.
The objects of the invention are achieved by employing a sensor to detect the relative motion between a knife mounted in a knife mount and a sharpening tool. The novel device also measures the power consumed during the cutting operation by employing a motor current monitor. Further advantageous embodiments and applications of the invention include the utilization of a mechanical sensor to measure other parameters such as conductivity or mechanical vibration. The sensor may also be provided to measure pressure or tension to determine the mechanical load on the knife, knife mount and/or the sharpening tool. An additional sensor may be provided for measuring the force between the sharpening tool and the knife. An evaluator can also be provided to evaluate the time dependence I(t) relationship signal of the sensor as illustrated in the accompanying graph in FIG. 3. This time dependence relationship (I)t can be utilized to evaluate sharpening of the cutting edge of the knife as well as the status of the sharpening tool. One way for checking the status of the sharpening tool is to utilize free grinding or the absence of forward feed during measurements of the time dependence (I)t relationship. The device of the invention may also be implemented by providing fully automatic feed for the novel apparatus as well as implementing the invention by operating the novel device utilizing the procedures heretofore described.
Consequently, a device according to the invention is characterized by providing a sensor for detecting contact between the sharpening tool and knife. Contact detection enables automatic movement, in which the sharpening position of the sharpening tool must be precisely set. The above disadvantages, i.e., unnecessary sharpening operations with respectively diminished service life for both the knife and sharpening tool, can thereby be avoided with the sensor according to the invention in semiautomatic machines, in which the knife is clamped and the sharpening process is started manually.
An excessive sharpening pressure, i.e., too great an application force between the sharpening tool and knife, which can cause the sharpening tool to move evasively, can also be avoided with a sensor according to the invention, thereby always ensuring that the cutting edge of the knife is actually sharpened.
In addition, a sensor according to the invention is envisioned to also be used to build a fully automatic device.
Contact between the sharpening tool and knife can be detected in various ways. For example, the current of an electric motor active during the sharpening process can be monitored. One example would be an electric motor that drives the sharpening tool. Contact between the sharpening tool and knife increases the frictional resistance, and hence the load on the motor. During the detection of motor current achievement of a contact point between the sharpening tool and knife manifests itself as a significant increase in current.
The motor current of the advancing device that guides the sharpening tool toward the knife can also be monitored. After the point of contact at which the knife and sharpening tool meet has been reached, a resistance is encountered in the advancing direction, which in turn manifests itself in the load placed on the accompanying electric motor as a rise in current.
One other way to detect contact between the sharpening tool and knife involves observing other secondary effects, e.g., a change in the pressure level of the supplied cooling lubricant. Such a pressure change can be detected by a pressure sensor, or, in another embodiment of the invention, via current detection once again, but this time relative to the pump motor for the cooling lubricant.
In addition, the time dependence of additional secondary effects, and hence the moment of contact between the sharpening tool and knife during the forward feed, can be ascertained during device operation. For example, the vibration behavior of the entire device could be monitored in this way. The conductivity or electrical resistance between the sharpening tool and knife could also be measured to determine when the sharpening tool came into contact with the knife. One other possible way of determining contact between the sharpening tool and knife would be to use a tension and/or pressure sensor, which can be attached to the sharpening tool or its mount, or to the respective knife, to measure the relevant forces. The moment of contact between the sharpening tool and knife inevitably gives rise to a respective mechanical load, which can be detected via the mechanical tension and/or pressure sensor.
The sensor according to the invention can be used to precisely set the advance, i.e., the path traversed by the sharpening tool against the knife. This enables a precise activation for the different advances that might be necessary when sharpening a knife. Advance is here understood as the respective position of the sharpening tool relative to the knife in a machining step, in which the various advances are initiated in sequence to grind a specific cross-sectional profile into the respective knife.
To grind in such a cross-sectional profile in optimal fashion, it is also advantageous if the sharpening pressure, i.e., application force between the sharpening tool and knife to be sharpened, can be precisely set. A sensor array according to the invention can also be used for this purpose without any greater additional effort.
In a particularly advantageous further development of the invention, an evaluator is additionally provided for evaluating the time dependence of the sensor signal. The sharpening process can be monitored and, if necessary, the sharpening pressure or advance can be controlled over this sensor signal time dependence.
Further, information about the status of the sharpening tool can also be gained over the sensor signal time dependence. This is the case in particular during fully automatic operation, since the required change of sharpening tool must either be indicated or automatically executed by the appropriate system.
To check the sharpening tool status, the time dependence of the sensor signal is preferably observed without advancing the sharpening tool. Therefore, the sensor signal is observed during the so-called free sharpening, in which material is ground from the respective knife until such time as the sharpening tool can essentially run freely again. The time dependence of this free sharpening phase can be used particularly well to check the status of the sharpening tool.
The invention is applicable to the most varied types of knives that require sharpening in meat-processing machines. For example, a so-called Wolf grinder wheel, which acts as a stationary counter-knife for a rotating shearing blade in a meat grinder, can be subjected to surface grinding using a device according to the invention, in which a mount must be provided for securing the Wolf grinder wheel in a plane-parallel manner, onto which a grinding wheel is lowered, or which is moved against a grinding wheel.
A so-called cutter knife can also be sharpened with a device according to the invention, in which a cutter knife mount that moves relative to the sharpening tool is advantageously provided for. To this end, a guide unit is preferably provided for a cutter knife mount to guide the cutter knife along stationary sharpening unit, as known for a semiautomatic device available on the market. However, the reverse arrangement would also be envisioned, i.e., a stationary cutter knife mount, along which a sharpening tool, e.g., grinding belt, is passed.